Process of producing light weight aggregate and the product thereof



Cal

Patented Sept. 24, 19 35 rnooass or. PRODUCING LIGHT ,WEIGHT nuances-reAND 11m rnonuc'r THEREOF Charles Knox Harding, deceased, late of LosAngeles, Calif., by Mabel T. Harding, San Diego, Calif., administratrix;said Charles Knox Harding, assignor, by mesne assignments, of one-halfto William F. MacGlashan, Pasadena,

Calif.

No Drawing. Continuation of applications Serial No. 375,585, July 2,1929, and Serial No. 426,182, February 5, 1930. This applicationSeptember 28, 1934, Serial No. 746,018. In Canada July 22 Claims. (01.25-156) This invention relates to an improved lightweight ceramicaggregate material for incorporation in hydraulic cement concrete orother building material and to the method of its manufacture. Alsoincluded within the scope of the invention is the concrete or buildingmaterial in which the new material is used. More particularly theinvention concerns the production, in gross quantities, of strong,light-weight, vesicular, ceramic bodies, mostof which are ofsubstantially the same size and shape.

' Ordinary concrete, because it is composed largely of gravel and sand,is inherently heavy. For this reason stress calculations for concretestructures must take into account the weight of the concrete and. thestructures must usually be made much stronger than would otherwise benecessary to carry the weight of the concrete. The difilculty is noteasily overcome by substituting other materials for concrete, becausethe strength and cheapness of concrete and the fact that it is fireproofand easily molded to the desired. shape are advantages not easily foundin a material of lighter weight that might be suggested forsubstitution.

Accordingly it is a purpose of the present invention to provide a newlight weight concrete in which all of the advantages of gravel concreteare retained but in which the disadvantage of excessive weight isovercome. Also it is an object of this invention to produce a lightweight concrete material that may be advantageously substituted for manybuilding materials other than gravel concrete, such for example asbrick, wood,

plaster board and asbestos products.

Besides accomplishing these objects the present invention provides asubstitute for the gravel in concrete, or an aggregate material forincorporation in other building materials, which is homogeneous,uniform, and strong, and makes the material that contains it a farbetter heat insulating material than ordinary building materials. Also,the bodies constituting the aggregate are symmetrical, usuallyspherical, and for that reason possess a maximum strength and a minimumof surface per unit of volume.

Furthermore, according to the invention herein described, a simple,expeditious, andeconomical method is provided for producing the newceramic aggregate material from readily available raw materials, andwith a minimum of equipment. By this method not only are gravel-sizelight weight bodies produced, but also a quantity of fines which can beused in place of sand in the subsequently formed concrete.

Broadly stated the new aggregate material is produced, in gross, byheating to the point of fusion quantities of preformed bodies comprisedof clay or similar earthy materialand constituents adapted to react toform a gas that will ex- 10 pand and vesiculate the bodies. To carry outthe process on the bodies without separating each body from all the restand yet without causing the bodies to coalesce or adhere together toform clinker-s, it is necessary to fuse the interior of 15 the bodieswhile maintaining the exteriors in a state in which they will not adhereto each other even though they are in contact. This may be .done inseveral ways. The bodies may be covered or coated with a material lesseasily fusible than the bodies themselves; powdered or granular materialless fusible than the bodies may be intermixed with them before they arefused so that the material will adhere to and cover the bodies as soonas their surfaces soften and become adherent; or the conditions of thekiln or furnace may be such as to form on the body a film or skin whichis less easily fusible than the remainder of the body. Any one of theseprocesses may be used or all three may be comblned to make certain thatthe bodies will not form clinkers and that a firm shell will be formedaround each of the bodies.

The basic raw material from which the bodies aretformed can be almostany of the earthy materials that are generally used for the productionof ceramic articles. Preferably, however, the starting material is anearth containing around one third alumina and two thirds silica whichgives a molecular ratio of approximately 10Si0223A12O3 which is aboutthat usually found in soil and common clay. Red burning clays of thischaracter, but containing 3 to 9% iron oxides, may be used. The firstconsideration after selecting the raw material is its fusing orsoftening temperature. Should this be terially above 2000 F., lime,magnesia, iron co pounds or material containing them or other fiuxingsubstances may be added pounds that will liberate a gas ,or gases in thepresence of carbon at temperatures around 2000 1''. Among such materialsare calcium sulphate, oxides of iron and mixtures of the two. As anexample 2% of gypsum (CaSOaBHz) may be added to an earth containing 3%iron.

oxide. Alternatively, fiuxing materials may be used that will have theeffect of reducing the softening temperature of the bodies and also willevolve a gas upon being heated under the proper.

conditions.

In addition to the substances already mentioned, 3 to 6% of carbonaceousmaterial, such, for example, as coal or coke, is introduced into themixture to cooperate with the substances mentioned above to expand andvesiculate the bodies when heated. The best results have been obtainedby using -80 mesh coal or coke, introducing it into a part of the batchwith enough water to form a thick slurry or very plastic mass, and thenadding the balance of the batch and mixing the whole thoroughly. Byusing 60-80 mesh carbonaceous material and heating not too rapidly thebodies may be caused to expand smoothly and evenly without breaking orclinkering as they will if the gas formed is liberated suddenly insidethe bodies. The gradual formation of gas may be aided by adding to themix several compounds liberating gases at different temperatures.Magnesium and calcium sulphate are examples of such compounds. If forany reason it is desired that the aggregate be light colored, a whiteburning clay should be used in conjunction with colorless fluxing andgas producing materials, such for example, as gypsum.

After the mixture of ingredients has been made, the composition ispugged, extruded, and shaped into bodies of the desired size in a mannerand by the use of equipment which is well known in the ceramicindustries. Ordinarily, the material is molded into uniformly sizedsmall balls or pellets of globular, rounded or at least rollable shapeand of a relatively small size so that they will expand when heated to asize suitable for direct incorporation into concrete or whatevercomposition is to contain them. Any size bodies can be made from thesize of the ordinary sand or fines used in concrete to a size evenlarger than the coarsest of aggregate materials in general use.

As an example of the expansion that takes place upon heating the bodiesa test of a mixture containing only 3% of ferric oxide may be given. Thematerial in the form of small pellets containing 60-80 mesh carbongranules was heated to 2000 F. in twenty minutes and maintained at thattemperature for twelve minutes during which it expanded to over threetimes its original volume.

Having formed but not yet burned the ceramic bodies, consideration mustbe given to the prevention of clinkering or adherence between the bodiesduring the heating. Affecting this consideration are the characteristicsdesired for the final product. For example, if extreme lightness is notthe main object, but strength is important, it is often advisable tocoat the bodies before heating with a silicious material which aids informing a solid, firm shell, or to heat the bodies in an oxidizingatmosphere which will burn out the carbon from the outer shell andprevent its vesiculating, reby making the aggregate stronger but hes Ifthe aggregate is to be used in concrete-the silicious chemically acidcoating makes for a better bond to the basic calcareous Portland 5cement. On the other hand, a lighter weight aggregate may be made byadding a refractory material in powdered form to the aggregate beforeheating, but without coating the bodies and without the use of anoxidizing atmosphere dur- 1 ing the heating.

Preferably, in forming a product for use in a hydraulic cement concretewhere extreme lightness is not as important as strength and simplicityof manufacture, all three of the processes for 15 preventing clinkeringare combined and a very uniform product having strong rather thickshells, and with practically no units fused together is formed.

As an example of the first mentioned method go of preventing adhesionbetween the bodies, namely the coating of the bodies with a refractorysubstance, formed rounded pieces of the fusible material, including thesubstances that will cause it to expand, may be coated on their outersur- 5 faces with a refractory, relatively lnfusible, ceramic materialsuch as a very fine silica, burned or raw fire clay rich in silica, orany other suitable inexpensive, ceramic, refractory material. A lightdiatomaceous earth consisting of silica in go an allotropic reactiveform makes an excellent coating for small bodies. The coating may beapplied bybeing blown onto the pugs or bodies as they leave theextruding device and are cut apart. Some of the coating material, whichis ,5 usually either in granular or powdered form, accompanies thebodies through the kiln. Preferably there is about 4 to 8% of thecoating material with the aggregate when it is fired. After firing, theexcess coating 'material is passed 40 through a grating and is returnedfor reuse, while the coating material adhering to the pugs has becomevitrified and welded into a practically continuous cover for thevesiculated bodies.

The firing may advantageously take place in 5 a long rotating kiln intoone end of which the aggregate is fed. The exhaust fuel gases leavethrough the same end, while the burned aggregate leaves and the unburnedfuel gases enter at the opposite end. An air lock is used to disa chargethe burned product so that pressure may be maintained on the incominggases. The kiln is adjusted so that the hottest part which isapproximately 2000 F. is near the center and the burned gases in leavingpreheat the incoming aggregate. This arrangement is important since ithas been found to effect a substantial economy in fuel.

During its progress through the kiln the mass of aggregate iscontinually stirred and the time consumed by the passage through thekiln is regulated to produce the desired degree of vesiculation. Onaccount of the number of variables involved this period of time is bestfixed by experiment, but is usually around 20 minutes. One aggregate sotreated expanded about 60% and was found well suited for use inreinforced concrete weighing somewhat over eighty-six pounds per cubicfoot.

Ordinarily, the aggregate bodies made in the above manner have strong,waterproof shells and can be combined with less than enough cement tofill the voids between the bodies so as to form a porous, light weightconcrete of great strength. With a larger proportion of cement a solid,nonporous, but heavier concrete results. A wall, the interior of whichis of strong porous concrete and the exterior of which is of solid,non-porous concrete, often possesses the exact characteristics desiredfor building purposes. Such a wall can be made by placing in a moldalternate layers of the two kinds of concrete.

The second process, namely the addition of refractory material to thebodies of the kiln, may be illustrated by the introduction into thekiln, along with the bodies, of a quantity of powdered or granularrefractory ceramic material, such for example as silica. During theburning the mass is constantly agitated or rolled by mechanical means sothat the outside of the bodies will pick up the silica rapidly as theyfuse and thus be prevented from welding together while at the burningoperation.

made by this process are especially useful in making solid concrete bythe use of at least enough cement to completely fill the voids betweenthe bodies, as such concrete does not require aggregate bodies of anygreatstrength because the strength is furnished by the cement matrix.

The process of the prevention of clinkering by the use of an oxidizingatmosphere during the heating of the bodies is chemically somewhatcomplex since it involves the oxidation of the compounds on the surfaceof the bodies and the resulting change in their fusing temperatures. Thetheory of the change is that ferric disllicate (Fezoafisioz) is formedby oxidation from ferrous silicate (FeaSizOs) which is originallypresent in the bodies. The former compound having a higher fusingtemperature forms a shell which does not fuse and hence preserves theidentity and individuality of the bodies. Ferrous sulphide is alsoconverted to the more refractory ferric oxide. Furthermore, thecarbonaceous material in the outer shell of the body is burned out andremoved before it can react with the other ingredients'to form a gas andvesiculate the shell. Therefore, the shell is practically non-porous.

Most of the shell forming reaction appears to take place in the range oftemperature from around 1100 F. to about 1800 to 1900 F. The extent ofthis reaction and hence the thickness and weight of the shell can begoverned by governing the length of time during which the shell remainsin that temperature range and by governing the composition of theatmosphere to which the aggregate is submitted during the If theatmosphere is only of an oxidizing nature during a short period theshell will be thin and light and vice versa. The temperature at whichthe oxidizing atmosphere is applied to the bodies also affects thecharacteristics of the shell and variation of these factors to produce ashell of any desired characteristics is within the scope of the presentinvention.

In preventing cohesion by the formation of an oxidized surface, the useof compounds causing expansion to take place gradually is of particularimportance, as rapid expansion will so break the surface film thatadhesion and clinkering are likely to result. As mentioned above,calcium and magnesium sulphates may be added in addition to the ironoxides.

Aggregate bodies made by any of the specific economical to manufactureas the raw material, 5

fueland manufacturing costs are all low. In forming concrete, less flnesand even less cement is required because of the spherical shape. Thespecific gravity of the bodies may be caused to be less than 1.3 ifdesired. 10

The foregoing description constitutes but a statement of the principlesof this invention together with a few examples and it is contemplatedthat adaptations, alterations and modifications in the process andproduct will be made 15 by those skilled in the art to meet the demandsof particular situations. The aggregate bodies may be made in almost anysize, they may be bound together by other materials than cement, coated"with other refractory substances than those named or their compositionsaltered all within the scope of thisinvention.

This application is a continuation of applications 375,585, filed July2, 1929, and 426,182, filed gregate which comprises dividing a batch ofexpansible, fusible raw ceramic material into relatively small pieces,coating the exterior surfaces 30 1 of said pieces with a refractorymaterial andsub- Jecting the coated pieces in bulk condition while incontact with other pieces to the action of hot gases until thetemperature of the fusible and expansible bodies of individual pieces israised 36 to effect the fusing and expanding of the pieces whileclinkering of the bulk is avoided by the refractory coatings.

2. The process of producing light weight aggregate from an expansible,fusible raw batch 4% mixture consisting largely of argillaceous materialwhich comprises dividing the mixture into relatively small pieces ofgenerally rounded formation, coating the exterior surfaces of the pieceswith a refractory relatively non-fusible mateas rial, subjecting thepieces in a loosely compacted bulk formation to the action of heatedgases by causing the gases to pass through the bulk, effecting thecontinued heating of the pieces in bulk until the fusible portionsthereof are softened 5% and the pieces expanded, and thereafterpermitting the pieces to cool with the result that they are in the formof light, vesicular, refractory coated bodies.

3. The method of producing a light vesicular 55' ceramic aggregate whichcomprises forming uniformly sized independent bodies from a plastic rawceramic batch of expansible, fusible and Weldable plastic material,providing and maintaining an exterior heat conducting contacting iii?surface on said units by coating the same with a more refractoryrelatively non-welding ceramic material, and subjecting a loosecontacting mass of said units to sumcient heat above the incipientwelding temperature of the interiors of said units 6% to expand andrender the units vesicular without otherwise expanding the morerefractory material while maintaining the units independent and freefrom clinkering with each other.

4. The process of rendering ceramic material 5% aggregate unitsvesicular without clinkering which comprises heating a contacting loosemass of independent units while maintaining a material more refractorythan the ceramic material at the points of contact, continuing theheating w of the units while maintaining the more refractory materialbetween the contacting portions thereof until the units have becomesoftened and expanded, whereby the units are rendered vesicular withoutclinkering.

5. Process of expanding and rendering vesiculose ceramic aggregate whichcomprises forming a plastic, fusible, expansible and weldable ceramicraw batch into approximately uniform sized individual units of generallyrounded formation, providing the individual units with an outer surfaceof material more refractory and less easily welded than the interiorthereof, heating the individual units while agitating the same in abodily moving mass to render the same vitrified and vesicular whilemaintaining the units independent and freely movable with respect to theother units of the mass body.

6. The. process of producing a light weight aggregate for concrete andthe like comprising forming argillaceous material which is capable ofbeing expanded by heat into a multiplicity of pellets, subjecting thepellets while in contact in bulk to the action of heat suflicient toeffect a softening and expansion thereof, and maintaining the identityof the individual pellets and avoiding substantial clinkering thereofduring the heating of the same by rendering the surfaces of the pelletssubstantially resistant to fusion at the temperatures utilized to effectthe pellet expansion at a stage in the process prior to the fusion andexpansion of the pellets.

'7. The method of producing an improved, light, hollow, ceramicaggregate which comprises forming from a plastic raw ceramic batch ofexpansible, fusible and weldable, plastic material, approximatelyuniformly sized, solid unit bodies of substantially uniform, roundedrollable shape,

of said weldable material and providing and maintaining an exterior heatconducting, nonvesiculatable contacting surface on said units of morerefractory and non-welding ceramic material and subjecting a largeloose, contacting mass of said units to sufficient heat above theincipient welding temperature of the bodies for suilicient time toexpand and completely hollow the units without welding or clinkeringtogether the fired ceramic units of the finished aggregate. 8. Theprocess of expanding, and hollowing solid ceramic aggregate whichcomprises forming a plastic, fusible, expansible, weldable, ceramic rawbatch into, approximately equal sized, solid individual units ofsubstantially uniform rounded shape, rollability and heatability,providing and maintaining an outer contacting surface of morerefractory, less easily welded, ceramic compounds on the outercontacting surfaces of said units, and firing a contacting, agitated,moving mass of said non-weldable aggregate, vitrifying and hollowing theunits without welding or clinkering the finished aggregate units.

9. The process of producing partly hollow ceramic aggregate units fromplastic material capable of being rendered vesicular which comprisesforming the plastic material into units and rendering the surfacesthereof more refractory than the interior body portions, effecting theexpansion of the units to render them vesicular by the application ofheat to the units while maintained in a mass, and continuouslysubjecting the units to treatment for maintaining the refractorysurfaces of the units intact during the expansion thereof.

. 10. The improved process of producing hollow ceramic structures whichconsists in forming unit structures of suitable size for use whenexpanded from plastic argillaceous, fusible, expansible materialcontaining compounds capable of generating gases in the presence ofcarbon ions derived from a tangible mass of incandescent carbon ca- 1pable of liberating carbon ions during considerable time, introducing amass of incandescable carbon into the body of said structures of fusiblematerial providing an exterior surface on said unit fusible structuressurrounding the carbon of 10 more refractory ceramic material which willbe united with said fusible bodies but will not reach its weldingtemperature when the bodies of the units are heated to the hightemperature necessary to soften, partly melt, and generate the 15 gaseswhich produce cells and bubbles within the fused body and expand thebody and render it hollow and subjecting a contacting mass of saidbodies and their surface layers to a temperature above the welding heatof the bodies and suf- 20 ficient to fuse and expand the bodies of theunits, generate gases therein and render them hollow but not sufficientto raise the refractory surface to its welding temperature and therebyrendering the units hollow without clinkering the 25 unit structures ofthe contacting mass of aggregate.

11. The process of producing light weight aggregate incharacteristically rounded vesticular generally globular particle formwhich comprises 20 preparing a raw batch of clay material containingabout 3% of ferric oxide and a substantial amount of ceramic fluxingmaterial to effect the batch mixture to partially soften at temperaturesof approximately 2000 F. with from 3 to 6% of 33 granular carbonaceousmaterial incorporated in a distributed condition into said batch,forming said mixtures into generally ball-like rollable pieces of a sizematerially smaller than the ultimate pieces to be produced, coating thefusible 40 and expansible pieces thus formed with an exterior coating ofrefractory ceramic material which will not soften and permit clinkeringof the same when a large mass of the coated pieces are in contact witheach other and heated to the high temperature necessary to thoroughlysoften and expand and render completely and uniformly vesicular theinterior of the preformed pieces except the outer shell, and thereaftersubjecting the individual rounded pieces while in bulk to the action ofheat to fuse and expand and render the individual pieces vesicularwithout effecting a clinkering of the material in bulk.

12. The process of producing light weight aggregate incharacteristically rounded vesicular generally globular particle formwhich comprises preparing a raw batch of clay material containing ironoxide and a ceramic fluxing material capable of softening the mixture attemperatures of approximately 2000 F. with from 3 to 6% of granularcarbonaceous material incorporated in a distributed condition in saidbatch, forming said mixture into generally ball-like rollable pieces ofa size materially smaller than the ultimate pieces to be produced, andthereafter subjecting the individual rounded pieces of aforesaidexpansible material to the action of heat while in bulk at a temperatureof approximately 2000 F. to effect the liberation of gases and cause theexpansion of the softened material to a generally rounded light weightaggregate, the material being heated in. bulk while being maintainedagainst clinkering.

13. The process of producing a partly hollow silica coated ceramicconcrete aggregate unit which consists in producing a refractory outersilicious surface or shell on the exterior surface of a relativelyfusible body of ceramic material capable of being rendered vesicular andcontaining ferruginous compounds before it is vesiculated and expandedand then eifecting the maintenance of the silicious refractory surfaceof the unit substantially intact while both its interior and exteriorare being expanded and while portions of the more fusible interiormaterial are being exposed at the surface of the unit.

14. The process of producing a hard strong solid waterproofouter.surface on a vesiculated partly hollow ceramic aggregate unitwhich consists in forming an outer layer of refractory character on saidbody before it is fused and expanded and. then maintaining said layer bythe addition of granular refractory material brought into contacttherewith during the time the surface of the body is being expandeddurging the vesiculating process.

.15. The process of producing a partly hollow ceramic aggregate unithaving a. hard strong outer surface, which consists in producing a bodyof fusible, iron containing ceramic material capable of being renderedvesicular, providing the body with a refractory less fusible outersurface layer of heat conducting ceramic material, and then graduallyvesiculating the body while maintaining and rebuilding the refractoryouter surface layer.

16. The process of producing silica coated vesicular aggregate whichconsists in adding a silica coating layer to the outer surface of avesiculatable ceramic body before it is expanded and then adding morerefractory ceramic material to the surface during the expanding andvesiculating operation.

17. The process of vesiculating ceramic aggregate consisting ofpreformed pieces of plastic clay and iron compounds containing carbon,which consists in subjecting while being stirred, rolled and agitated acontacting mass of said loose pieces to I gradually increasingtemperature and causing them to gradually enlarge while surrounded by anoxidizing furnace atmosphere to assist in maintaining a refractorynon-welding outer surface on said pieces by oxidizing the ferrosilicatesand transforming the ferric compounds during the gradual vesiculatingand expanding operation thereby maintaining intact a refractory andnon-welding contacting exterior surface, and 5 finishing the burning andexpanding operation without clinkering.

18. An aggregate material, the individual units of which compriseartificially expanded, cellular, fired, ceramic material surrounded byan exterior surface of more dense material serving to strengthen theunits and retard the entrance of moisture into the interior thereof.

19. An aggregate material, the individual units of which compriseartificially expanded, cellular, fired, ceramic material surrounded byan exterior surface of silicious material serving to strengthen theunits and retard the entrance of moisture into the interior thereof.

20. An aggregate material, the individual units of which compriseartificially expanded, vesicular, fired, ceramic material surrounded byan exterior surface of more refractory material serving to strengthenthe units and retard the entrance of moisture into the interior thereof.

21. An aggregate material, the individual units of which arecharacteristically of a generally globular shape and of such size as tomake the material necessarily a bulk product, said units comprisingartificially expanded, cellular, fired, ceramic material surrounded byan exterior surface of more dense material serving to strengthen theunits and retard the entrance of moisture into the interior thereof.

22. An aggregate material, the individual units of which arecharacteristically of a generally globular shape and of such size as tomake the material necessarily a bulk product, said units comprisingartificially expanded, cellular, fired, ceramic material surrounded byan exterior surface of more dense material serving to strengthen theunits and retard the entrance of moisture into the interior, said bodieshaving a specific gravity of less than 1.3.

MABEL T. HARDING, Administratria: of the Estate of Charles K. Harding,Deceased.

